DE102013008826A1 - Method for operating an internal combustion engine - Google Patents

Abstract

A method of operating an internal combustion engine, comprising an internal combustion engine (10), a fresh gas train, an exhaust gas line, an exhaust gas turbocharger with a compressor (24) integrated into the fresh gas train and a turbine (22) integrated into the exhaust gas line, as well as an integrated into the fresh gas train, preferably an electrically driven auxiliary compressor (28), wherein a scavenging is performed by purging in a combustion chamber of the supercharger (24) at an overpressure in the fresh gas train downstream of the compressor (24) compared to the pressure in the exhaust line upstream of the turbine (22) Internal combustion engine existing combustion gas by a simultaneous opening of the combustion chamber associated intake valve and the combustion chamber associated exhaust valve of the engine (10), is characterized in that at a load jump first of the auxiliary compressor (28) is activated and then the scavenging is performed.

Description

The invention relates to a method for operating an internal combustion engine according to the preamble of claim 1.

It is known to equip internal combustion engines, such as those used for driving motor vehicles, with a charge by, for example, exhaust gas turbochargers. As a result of the charging, the pressure of the fresh gas supplied to an internal combustion engine of the internal combustion engine is increased, which increases the filling of the combustion chambers, thereby increasing the amount of fuel that can be converted per working cycle and consequently the power of the internal combustion engine. In addition, the efficiency, in particular of a diesel internal combustion engine, can be increased by charging.

The increase in performance of an internal combustion engine by means of an exhaust gas turbocharger is limited at low speeds, inter alia, by the so-called surge limit of the compressor of the exhaust gas turbocharger. The surge line represents the transition from stable to unstable operating range, wherein in the unstable operating range, the promotion of the fresh gas mass flow, triggered by a regularly occurring at the entrance of the compressor impeller stall is periodically interrupted.

A shift of the surge limit to lower fresh gas mass flows can in principle be achieved by compressors with a smaller throughput, which are then limited in terms of the maximum throughput until reaching the Stopfgrenze. This problem is often circumvented in practice by the fact that a multiple charging is provided, either two comparatively small exhaust gas turbocharger are connected in parallel, which together provide a sufficient flow rate for the fresh gas mass flow, or a small and a large exhaust gas turbocharger are connected in series, wherein at low Exhaust gas and fresh gas mass flows only the smaller and at very high exhaust gas and fresh gas mass flows only the larger of the two turbochargers is operated.

It is also known, instead of charging by means of several exhaust gas turbochargers to support an exhaust gas turbocharger by a mechanically or electrically driven auxiliary compressor, wherein electrically driven auxiliary compressors (so-called "e-booster") have the advantage of a simple design and good on and Ausschaltbarkeit. This makes them well-suited for temporary support only. A disadvantage of e-Boosters is the high consumption of electrical energy, which, in order to limit the currents occurring, must be provided regularly with an electrical voltage that is above the usual 12 V or 24 V of a conventional electrical system of motor vehicles.

Furthermore, from the US 2009/0194080 A1 known in a diesel internal combustion engine to implement a so-called "scavenging", in which by overlapping the opening times of the intake and exhaust valves of the individual cylinders in times of local overpressure in the fresh gas train compared to the local pressure in the exhaust gas exhaust gas in the cylinders has remained, and possibly dissipate some fresh gas into the exhaust system. In the internal combustion engine according to the US 2009/0194080 A1 this is done by switchable additional cam for the intake valves, which are activated during operation of the internal combustion engine in a dedicated operating range (low speeds with medium to high loads) and cause additional opening of the intake valves during the exhaust stroke and thus in overlap with an opening of the exhaust valves , The scavenging on the one hand improves the filling of the combustion chambers, since the exhaust gas contained therein is replaced by fresh gas. In addition, the pumping limit of the compressor of the exhaust gas turbocharger can be shifted by the increased gas flow rate through the internal combustion engine.

From the US 2011/0174249 A1 is still known, based on the from the US 2009/0194080 A1 known system to change the opening times of the intake valves during the intake stroke so that they either reach their closed position before or after the bottom dead center of the piston. Thereby, a reduction of the exhaust gas pressure is to be achieved, whereby the pressure gradient between the fresh gas train and the exhaust line, which is required for the scavenging, can be increased. This should allow the execution of scavenging at low loads. Alternatively, in the US 2011/0174249 A1 moreover, to provide an auxiliary compressor which, when operating the internal combustion engine with low to medium loads, provides for the increased intake manifold pressure required for the scavenging. The additional compressor should be mechanically or electrically driven.

From the DE 199 08 286 A1 Furthermore, a valvetrain is known in which a tubular cam carrier is arranged rotationally fixed and axially displaceable on a basic shaft. The cam carrier forms axially offset two cams with different cam tracks. By the axial displacement of the cam carrier on the fundamental shaft, a gas exchange valve can be actuated by the differently shaped cam tracks in different ways. Such a valvetrain is also suitable for an additional opening of the inlet valve during the exhaust stroke to realize scavenging.

Based on this prior art, the invention has the object, in an internal combustion engine, in particular diesel internal combustion engine, to achieve an increase in performance at low speeds by increasing the maximum torque at these speeds.

This object is achieved by a method for operating an internal combustion engine according to independent claim 1. Advantageous embodiments of the method according to the invention are the subject of the dependent claims and will become apparent from the following description of the invention.

A method according to the invention for operating an internal combustion engine which comprises an internal combustion engine, a fresh gas train, an exhaust gas line, an exhaust gas turbocharger with a compressor integrated in the fresh gas train and a turbine integrated in the exhaust gas line, and a preferably electrically driven auxiliary compressor integrated into the fresh gas train, wherein (temporarily) scavenging is performed by purging combustion gas present in a combustion chamber of the combustion engine by simultaneously opening (at least) one of the combustion chamber at an overpressure in the fresh gas train downstream of the compressor compared to the pressure in the exhaust line upstream of the turbine Inlet valve and (at least) one of the combustion chamber associated exhaust valve of the internal combustion engine takes place, is characterized in that at a load step, first the additional compressor is activated and then the scavenging durchgef is led.

The invention is therefore based on the idea of advantageously combining the advantages which an additional compressor on the one hand and the scavenging on the other can have on the filling of the combustion chambers and the surge limit of the compressor of an exhaust gas turbocharger. In this case, the additional compressor is used for after a load jump, d. H. a spontaneous significant increase in the load request to the internal combustion engine to quickly generate a relatively high pressure level in the fresh gas train, which improves the desired filling of the combustion chambers. This creates a pressure level that allows scavenging to be performed. As soon as this pressure level is reached and the displacement of the surge limit of the compressor initiated by the additional compressor can be maintained substantially by means of scavenging, the additional compressor can be switched off again. The temporary pressure increase by the additional compressor can then be replaced by a higher pressure ratio from the exhaust gas turbocharger, since the pumping limit is no longer limiting or the operating point of the compressor is stable in the compressor map by the increased gas flow by means of scavenging. Due to the short-term operation of the additional compressor whose energy consumption, in particular the absorption of electrical energy in an electrically driven auxiliary compressor is limited. This also makes it possible to use a particularly electrically driven additional compressor, which can be designed so that it can apply the required maximum power only for a short time and not in continuous operation. The additional compressor can thus be designed comparatively small and inexpensive.

Accordingly, it can be provided in particular that the additional compressor is deactivated again before or at the beginning of the scavenging. Deactivation before the beginning of the scavenging should ensure that the pressure level necessary for the execution of scavenging in the fresh gas train (behind the compressor of the exhaust gas turbocharger and in particular directly in front of the internal combustion engine, in particular in an intake manifold of the internal combustion engine) until the initiation of scavenging is maintained (eg by a run-on of the deactivated additional compressor) or upright.

Accordingly, it can be provided with particular advantage that the additional compressor is deactivated if at least temporarily a pressure gradient enabling the scavenging between the fresh gas train and the exhaust line is set, in particular the local pressure gradient from p ₂ (intake pipe pressure) to p ₃ (exhaust gas backpressure upstream of the turbine of FIG Exhaust gas turbocharger) is relevant.

The method according to the invention can be carried out, in particular, when the load jump occurs at speeds of the internal combustion engine of between approximately 800 l / min and approximately 2000 l / min, since in this speed range, in combination with the initially low load, the exhaust gas turbocharger and Frischgasmassenstroms not fast enough for a sufficient pressure increase in the fresh gas line, which is also necessary for the scavenging, can provide. This pressure increase can then be adjusted according to the invention quickly by means of the additional compressor.

The invention will be explained in more detail with reference to an embodiment shown in the drawings. In the drawings shows:

1 an internal combustion engine that can be operated by a method according to the invention;

2 schematically the effect of the additional compressor on the operation of the compressor of the exhaust gas turbocharger;

3 schematically the effect of scavenging on the operation of the compressor of the exhaust gas turbocharger; and

4 FIG. 2: schematically the increase of the torque of the internal combustion engine of the internal combustion engine by the operation according to a method according to the invention.

In the 1 is greatly simplified an internal combustion engine shown, which can be operated according to a method of the invention. By means of the internal combustion engine, for example, a motor vehicle can be driven.

The internal combustion engine comprises an internal combustion engine 10 , which operates on the diesel principle. The internal combustion engine 10 forms in a composite of cylinder crankcase and cylinder head several (eg four) cylinder 12 out. The cylinders are inlet side with a suction tube 14 a fresh gas line and the output side with an exhaust manifold 16 an exhaust line gas leading connected. In a known manner is in combustion chambers, by the cylinders 12 in connection with in the cylinder 12 trained up and down piston, air burned with fuel. The resulting exhaust gas is discharged through the exhaust line. The supply of the air into the combustion chambers and the removal of the exhaust gas from the combustion chambers is via at least one inlet valve 18 and an exhaust valve 20 controlled by a non-illustrated valve train of the internal combustion engine 10 be operated.

The internal combustion engine further comprises an exhaust gas turbocharger. This has a turbine integrated into the exhaust system 22 and a compressor integrated into the fresh gas train 24 on. An impeller of the turbine driven in rotation by the exhaust gas flow 22 drives over a wave 26 an impeller of the compressor 24 at. The thus caused rotation of the impeller of the compressor 24 compresses the fresh gas passed through it.

Upstream of the compressor 24 the exhaust gas turbocharger is an additional compressor 28 integrated into the fresh gas train. The additional compressor 28 is powered by an electric motor 30 driven. Alternatively, the additional compressor 28 but also downstream of the compressor 24 be arranged.

At low speeds of the internal combustion engine 10 Among other things, the maximum torque output by the latter is due to the surge limit of the compressor 24 limited the exhaust gas turbocharger. This surge limit is shown in the diagrams according to the 2 and 3 shown. The diagrams show the pressure ratio p ₂ / p ₁ (p ₂ : pressure downstream of the compressor, p ₁ : pressure upstream of the compressor) above the mass flow ṁ through the compressor 24 on. The bounded by the dashed line area is the compressor map, within which the compressor can be operated stably. The pumping limit is the left-side, ie to low mass flows towards the limit of the compressor map.

The dot-dash line in the diagrams of 2 and 3 illustrates the operation of the compressor, as in an exemplary internal combustion engine according to the 1 with deactivated booster compressor and without the execution of scavenging would result. It turns out that over a relatively large area the operation would have to take place or take place outside the surge limit of the compressor map.

The solid line in the 2 shows the positive effect that the additional compressor 28 on the operation of the compressor 24 of the exhaust gas turbocharger can have. The additional compressor 28 caused by the arrangement on the low pressure side of the compressor 24 a pressure increase on this side, ie from p ₁ . This reduces the ratio of p ₂ to p ₁ , so that the operating characteristic curve shifts downwards while the mass flow gleich remains constant, thereby approaching the surge limit or even being within the compressor characteristic map.

The solid line in the 3 shows, however, the positive effect that the scavenging on the operation of the compressor 24 of the exhaust gas turbocharger can have. The scavenging causes an increased mass flow ṁ by the internal combustion engine 10 and thus also by the fresh gas train. Due to the larger mass flow ṁ through the compressor shifts its operating characteristic to the right and is thus closer to the surge line or even within the compressor map.

According to the invention, during operation of the internal combustion engine at low speeds (about 800 l / min to about 2000 l / min), provided that in a load jump spontaneous, significantly increased load requirement is given, first the additional compressor 28 to activate. This very quickly causes an increase in pressure in the fresh gas line and thus an improved filling of the combustion chambers, which can lead to an increase in the maximum torque of the internal combustion engine by a corresponding increase in the fuel converted into the combustion chambers. Due to the positive effect on the operation of the compressor 24 the exhaust gas turbocharger is also achieved that this very fast itself can provide an increase in pressure, which makes the use of scavenging possible. Namely locally higher pressure in the intake manifold (p ₂ ) than in the exhaust manifold (p ₃ ) is required.

Once this pressure gradient is reached, it is intended to initiate a scavenging. For this purpose, by means of the valve train, for example, as a switchable valve train according to the DE 199 08 286 A1 may be formed, an additional opening of the intake valves 18 realized during the respective outlet stroke. Due to the valve overlap generated in this way, exhaust gas which has remained in the combustion chambers can be replaced by fresh gas. As a result, not only the filling of the combustion chambers with fresh gas but also the gas flow rate through the internal combustion engine is improved. The increased gas flow rate can, as shown by the 3 described the operation of the compressor 24 of the exhaust gas turbocharger, which in turn can improve the filling of the combustion chambers.

According to the invention, the additional compressor 28 to use after a load jump from low speeds to reach the necessary pressure gradient for performing scavenging as quickly as possible and to improve the filling of the combustion chambers, as long as a filling improvement by the scavenging is not yet available. Once scavenging is initiated, the booster compressor is deactivated to limit its energy intake. Its positive influence on the filling of the combustion chambers is then taken over by the scavenging, as shown schematically in FIG 4 is shown.

There, the dot-dash line indicates the course of the torque M (on the vertical axis) over the time t (on the right axis), provided that the internal combustion engine would be charged out of an operating point with low load and low speeds both without additional compression and without scavenging. The solid line shows the corresponding course of the torque with both measures in the combination according to the invention. The first increase in torque is due to the operation of the booster (see left-hatched area), while this is later held up by the scavenging (see right-hatched area). With the beginning of the scavenging the additional compressor is deactivated. Its influence on the filling and thus the torque is reduced continuously in a transition region (within which the additional compressor runs out).

LIST OF REFERENCE NUMBERS

10

internal combustion engine

12

cylinder

14

suction tube

16

exhaust manifold

18

intake valve

20

outlet valve

22

turbine

24

compressor

26

wave

28

auxiliary compressor

30

electric motor

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 2009/0194080 A1 [0006, 0006, 0007]
• US 2011/0174249 A1 [0007, 0007]
• DE 19908286 A1 [0008, 0030]

Claims (5)

Method for operating an internal combustion engine with an internal combustion engine, 10 ) a fresh gas train, an exhaust gas line, an exhaust gas turbocharger with a compressor integrated into the fresh gas train ( 24 ) and a turbine integrated in the exhaust gas line ( 22 ), as well as with an additional compressor integrated into the fresh gas train ( 28 ), wherein a scavenging is performed by at an overpressure in the fresh gas line downstream of the compressor ( 24 ) compared to the pressure in the exhaust line upstream of the turbine ( 22 ) a purging of in a combustion chamber of the internal combustion engine ( 10 ) combustion gas by simultaneously opening an inlet valve ( 18 ) and an exhaust valve ( 20 ), characterized in that at a load step first of the additional compressor ( 28 ) is activated and then the scavenging is performed. Method according to claim 1, characterized in that the auxiliary compressor ( 28 ) is deactivated again before or at the beginning of the scavenging. Method according to claim 2, characterized in that the auxiliary compressor ( 28 ) is deactivated when at least temporarily a pressure gradient enabling the scavenging between the fresh gas train and the exhaust gas line is set. Method according to one of the preceding claims, characterized in that the auxiliary compressor ( 28 ) is activated only when the load jump at speeds of the internal combustion engine ( 10 ) between about 800 1 / min and about 2000 1 / min. Method according to one of the preceding claims, characterized in that the auxiliary compressor ( 28 ) is electrically driven.

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